The present invention relates to a dust-removing synthetic resin filter for use in air conditioners or dust collectors, and more particularly, relates to a dust-removing synthetic resin filter capable of so-called clean combustion which is free from discharge of harmful substances upon incineration thereof, and is advantageous from the standpoint of preventing environmental pollution.
Dust-removing filters for use in air conditioners or dust collectors of buildings, factories or home (hereinafter referred simply to as "filter") have been periodically replaced with new ones at intervals of one to several years according to a degree of deterioration or contamination of the filters in order to maintain a good performance thereof.
Hitherto, since many of such filters are made of glass fibers, most of the used filters have been buried under the ground as wastes upon disposal thereof.
However, in association with the wide spread of air conditioners or the like, the amount of waste filters have been increased year by year, thereby causing problems concerning necessity of ensuring the space for waste disposal (landfill), occurrence of environmental pollution after the landfill or the like. For these reasons, there has been a recent tendency that the used filters are burned for disposal to reduce a volume thereof.
In consequence, it has been attempted to replace the glass fibers as a raw material of the filters with synthetic resin fibers made of polyesters or polypropylene. Incidentally, the filters comprising these synthetic resin fibers may contain glass fibers in an amount of not more than about 10% by weight in order to ensure a good dust-collecting efficiency (hereinafter referred to as "synthetic resin filter").
However, since these synthetic resin filters contain as a binder, acrylic resins or vinylidene chloride resin and further contain chloride compounds or the like in order to impart a fire retardant property to these filters, a large amount of hydrogen chloride gas or sulfur dioxide gas is generated upon burning thereof. Accordingly, it has been required to take a measure for treating such hydrogen chloride gas or sulfur dioxide gas, or there have been caused problems such as damage to incinerators due to a high-temperature combustion heat, corrosion of ducts or exhaust ventilating fans or the like.
On the other hand, it has also been attempted to recover energies generated upon the burning of the synthetic resin filters, and especially, studies on a so-called thermal recycle for converting such energies into an electric power, have proceeded.
In the thermal recycle, when hydrogen chloride is present in the combustion gas, the corrosion of steam-generating portions (heat exchangers or the like) has been caused.
For this reason, at present, there have been used a method of purifying the combustion gas to remove harmful substances therefrom (e.g., see Japanese Patent Application (KOKAI) No. 56-122894 (1981)).
More specifically, in Japanese Patent Application (KOKAI) No. 56-122894 (1981), there is described a method for recovering a fuel from waste plastics which comprises mixing waste plastics with a granulating material containing an alkaline calcium compound to reduce the volume of the waste plastics and solidify the waste plastics; subjecting the resultant solids to thermal decomposition; and neutralizing, fixing and removing hydrogen chloride generated upon the thermal decomposition by the above calcium compound.
The reaction for fixing the hydrogen chloride gas or the sulfur dioxide gas in the combustion gas by the calcium compound, proceeds is set forth below.
&lt;Fixing reaction of hydrogen chloride gas&gt;
Synthetic Resin+Heat.fwdarw.Hydrogen Chloride (HCl)+ PA1 CaCO.sub.3 +2HCl.fwdarw.CaCl.sub.2 +H.sub.2 O+CO.sub.2 PA1 &lt;Fixing reaction of sulfur dioxide gas&gt; PA1 Synthetic Resin+Heat.fwdarw.Combustion Gas+SO.sub.2 PA1 2SO.sub.2 +O.sub.2.fwdarw.2SO.sub.3 PA1 CaCO.sub.3 +SO.sub.3.fwdarw.CaSO.sub.4 +CO.sub.2
Decomposition Gas (Combustible Gas)
The conversion rate of the hydrogen chloride into calcium chloride in the above-mentioned reaction is slower than the generation rate of the hydrogen chloride by decomposition of the synthetic resin, so that it is not possible to immediately fix the hydrogen chloride gas generated. In consequence, in Japanese Patent Application (KOKAI) No. 56-122894 (1981), it has been recommended that lime is used as a dehydrochlorinating agent in such an amount several times a stoichiometric amount thereof (Ca/2Cl=1).
However, in the case of producing the synthetic resin filter, it is disadvantageous that lime is present in the synthetic resin fibers or the filter material. Especially, when the lime is present in a large amount (enough to fix the hydrogen chloride gas generated), there arise problems such as a deteriorated filter efficiency, e.g., increase in pressure loss or deterioration in dust retention force; wear of fiber-producing apparatuses; deterioration in strength of fibers produced; increase in amount of ashes generated when used filters are burned; or the like.
Further, when an apparatus for purifying a combustion gas is to be connected to a steam generator in order to prevent the steam generator from being corroded in the thermal recycle, the temperature of the steam generator is lowered so that the energy recovery is limited to a low level. As a result, the conversion percentage of the recovered energy into an electric power is lowered, and it becomes difficult to accomplish the aim of the thermal recycle.
For these reasons, there has been studied a method of accelerating a reaction for the production of calcium chloride such that lime and hydrogen chloride can be reacted at such an increased reaction rate corresponding to the reaction rate of producing the hydrogen chloride by the decomposition of resin components, thereby enabling hydrogen chloride gas or sulfur dioxide gas generated upon burning of the synthetic resin to be immediately fixed by lime, etc., and preventing these gases from being scattered into an exhausted combustion gas. More specifically, there has been studied a catalyst for more rapidly transforming the hydrogen chloride gas generated into calcium chloride.
Among oxides of transition elements or the like, as catalysts capable of efficiently reacting hydrogen chloride gas generated in the course of heat-decomposition of the synthetic resin with dehydrochlorinating agents such as lime, there are known copper oxides or iron oxides. These oxides can absorb and activate the hydrogen chloride gas generated, and then serve for coupling the gas with the dehydrochlorinating agent such as lime. Therefore, these oxides can capture hydrogen chloride or sulfur dioxide with a high efficiency, and cause these gases to exist in the form of CaCl.sub.2 or CaSO.sub.4 in combustion ashes.
However, in the case where the copper oxides are burned for disposal, the oxides remain as ashes. Accordingly, in view of the toxicity, the use of the copper oxides is practically inappropriate.
As a result of the present inventors' earnest studies, it has been found that by using as a filter material, synthetic resin fibers having iron oxide particles having a high catalytic property for accelerating the fixing of hydrogen chloride gas, etc., the hydrogen chloride gas can be more rapidly fixed as calcium chloride and the sulfur dioxide gas can be more rapidly fixed as calcium sulfate. The present invention has been attained on the basis of the finding.